Viracept contamination could be more widespread says FDA

The FDA has said that the recent contamination in the US of Pfizer's HIV/AIDS drug, Viracept (nelfinavir), could be more widespread than first thought.

On September 10 the FDA revealed that "as a consequence of the recall in Europe, Pfizer tested its drug supply of Viracept. Most of the testing has shown ethyl methanesulfonate (EMS) levels within final acceptable limits".

As a result, the FDA and Pfizer have agreed to temporary limits of exposure of this impurity to allow for continued use in populations where the benefits of taking Viracept outweigh potential risks.

The manufacturing process is reportedly being refined to ensure that EMS levels meet final acceptable limits.

However, this could merely be the surface of a more widespread problem, according to a representative of the FDA's Center for Drug Evaluation and Research (CDER), who suggested that EMS could be in a number of drug products that have been on the market for years.

In an interview with US-PharmaTechnologist.com, Dr Jeff Murray, deputy director of the CDER's division of antiviral products, said: "There are several drug products on the market that have mesylate, besylate or tosylate saltsÖ these are the type of drug salts that could involve this process impurity, ethyl methanesulfonate."

"This involves potentially several different drug products that could finally come under the final [EMS] specification," Murray continued.

Advice for patients
New advice has been issued by the FDA stating that paediatric patients who need to begin HIV treatment should not start on regiments containing Viracept.

However, paediatric patients who are stable on Viracept can continue treatment, as the FDA and Pfizer believe the risk-benefit ratio remains favourable.

Pregnant women are being advised to switch to another treatment.

Viracept (which is produced and marketed by Roche in Europe) was recalled in May 2007 after batches were contaminated by EMS, a genotoxic substance, in its Swiss manufacturing plant.

The high EMS levels were caused by human errors in cleaning processes that left large amounts of excess ethanol in the process machinery. This subsequently reacted with chemicals during the drug's manufacture leading to a large spike in EMS levels in certain batches of Roche's Viracept product. Lower levels of EMS are usually present in the drug.

Roche's marketing license for Viracept was officially suspended in August, and will not be reinstated until the EU Commission receives new data.

At the time Roche was quick to point out that the US, Canada and Japan were not affected.

Around 45,000 patients worldwide are on Vircept, with 19,000 of those in Europe.